Process for producing gases



Patented June 2, 1936 UNITED STATES PATENT oFrlcE 2.04am mocEss ron. monocmo oAsE-s Augustus B. Kinzel, Flushing. N.. Y., assignor, by mesne assignments, to Union Carbide and Carbon Corporation. a corporation o! New York Application June 22, 1933, Serial No. 677,074

2 Claimd (Cl. 2H)

The invention relates to the production of gases for use as an atmosphere in which to heat treat metals and alloys, and has for its chief object the provision of a new and useful process for 5 producing gases for bright annealing.

Heat treatment of metals and alloys is usually done in the presenceof air, with the result that the surface of the metal is discolored or even attacked suiliciently to form a scale which must l l be removed by pickling, grinding, or sand-blasting. A desire to eliminate the' damage to metal surfaces during heat treatment, especially during annealing, has led to the use o1' reducing or relatively inert atmospheresduring the treatment. l5 Thus, illuminating gas, natural gas fractions,

carbon monoxide, cracked ammonia, pure hydrogen, and pure nitrogen, have each been proposed for the purpose. However, all of these gases have one or more of the disadvantages of being 20 toxic, explosive, flammable, expensive, or ineective to prevent the surface discoloration of all explosive when mixed with air in any proportions.

35 Mixtures of nitrogen and hydrogen containing up to about 7% hydrogen, nonfiammable 1n air, and mixtures of nitrogen and hydrogen containing up to about 15% hydrogen, non-exdevice which will produce hydrogen substantially plosive in air, each substantially free from oxy- 40 gen, oxygen-containing gases, and gases which tend to deposit carbon on the work, are admirably suited for bright annealing and other high temperature treatments of metals and alloys.

It is an object of the invention to provide a 45* practicable process for producing substantially pure mixtures of hydrogen and nitrogen for` bright annealing.

A further object of the invention is' to provide a practicable, efficient, and relatively inexpen-` 50 sive process for producing for bright annealing substantially pure mixtures of hydrogen and nitrogen, using hydrocarbons, preferably natural gas fractions, as the raw material.

These and further objects of the invention are i attained in the press which wm be resentedl hereinbelow, with reference .to the drawing, in

which The single iigure is a diagrammatic flow sheet 'of the process.

The processl in the preferred form shown in 5 the drawing comprises thermally cracking a por- 'tion of gaseous or vaporized hydrocarbons completely to carbon and-hydrogen, separating the hydrogen from the carbon, cooling and cleaning thev hydrogen and storing it temporarily in a 10 holder; burning another portion ofv hydrocarbons with air to produce a mixture containing nitrogen, carbon dioxide, and Water, and cooling the combustion products; Vpassing a portion of hydrogen `from the holder in heat exchange relav tionship to, but out of direct contact with, a portion of the cooled combustion products, whereby the hydrogen and combustion products are brought to substantially the same temperature; thoroughly mixing in predetermined proportions 2@ hydrogen and combustion products-at substantially the same temperature; scrubbing the mixture to remove substantially all of the carbon dioxide, refrigerating the mixture to remove most of the water; desiccating the mixture to remove substantially all traces oipmoisture; and l sub'- jecting the mixture to a nalpurication treatment with a: suitable active material to remove substantially all traces of oxygen-containing gases. While it will usually be desired to add the hydrogen to the combustion products before the carbon dioxide scrubber, under some conditions it may be desired to mix the hydrogen with the nitrogen after the latter has been scrubbed or even after the nitrogen has been dried or purle..

ned.

Although any eicient hydrocarbon cracking free from hydrocarbons and oxygen may be used .40 in the process ofthe invention, I prefer to use the cracking furnace and its auxiliary apparatus .disclosed and described in the copending appli- Adrogen substantially'free from hydrocarbons, 55

carbon monoxide and oxygen, I prefer to use the method and apparatus described in the copending application of John J. Egan, filed June 22, 1933, Serial Number 677,047, wherein a mixture of hydrocarbons and air in predetermined proportions are ignited,y and the combustion products are passed over an oxidation catalyst to complete the oxidation of the carbon. v

For the final purification step, the gas may be passed over or through anyv actively oxidizable material, for example, alkali metals, alkaline earth metals, or non-volatile active organic reducing agents; but I prefer to use a molten partial eutectoid mixture of metallic sodium and potassium mixture, as described in the copending application of Hendrik Erasmus, filed November'17, 1933, Serial Number 698,550.

The scrubbing device for removing carbon dioxide may be a packed tower, or a tower provided with trays or trays and bubble-caps, and the scrubbing liquid may be a solution of a carbonate, an amine or other suitable alkaline or basic liquid. If desired, the scrubbing may be done under pressure, in known manner. A scrubbing liquid which may be regenerated by stripping out the carbon dioxide, and recirculated through the scrubber, is to be preferred.

The refrigerator may consist of cooling pipes containing cold brine, over the outer surface of which pipes the gas is passed; or the gas may be passed in counter-current flow to, and in direct contact with, a stream of cold brine.

The desiccator may consist of a tower packed with a solid which will absorb or react with moisture, for example, calcium carbide, calcium oxide, or sodium hydroxide.

Auxiliary apparatus such as gas mixers, coolers, and heat exchangers, may be standard types and designs.-

While the above described process steps are preferred, modifications thereof are possible. Almost any vapcrizable and combustible fuel, for `instance, illuminating gas, natural gas, natural gasfractions, producer gas, or petroleum fractions, may be used as fuel in the production of nitrogen and carbon dioxide; or a part of the hydrogen 'obtained from the cracking stage may be used as the fuel. If hydrocarbons are used in the combustion stage, an excess of hydrocarbons may be used so as to produce thereby a part of the hydrogen desired in the final annealing gas. -In some circumstances it will be possible and desired to use a refrigerated scrubbing liquid in the CO2 scrubber, rather than to use a separate refrigerating device; or to eliminate the desiccating step or the nal purification step, or both. However, although each of these variations may be suitable under certain circumstances and conditions, they do not provide as satisfactorily flexible or efficient a process as the preferred form for producing mixtures of great `nitrogen-containing gas, whereby and water.

monoxide, oxygen, and hydrocarbons; intermi-tl tently thermally cracking hydrocarbons in the absence of air, steam, or other .Oxygen-containing gas, to produce hydrogen free from more than traces of oxygen, and hydrocarbons; ternporarily accumulating the hydrogen so produced to provide a source from which hydrogen can be withdrawn continuously; passing a stream of said hydrogen in heat exchange relationship to, but not in direct Contact with, a stream of said the streams are brought to substantially the same temperature; thoroughly mixing in predetermined proportions the said hydrogen and nitrogen-containing gases to form a mixture in which the hydrogen is not more than about 15% of the mixture; scrubbing the last-mentioned mixture with a basic solution whereby to remove substantiallyall carbon dioxide; refrigerating the scrubbed mixture to remove the major part of the Water; and finally desiccating the gas.

l 2. Continuous process for producing bright annealing gases, which comprises withdrawing a supply of hydrocarbon gas from a suitable source or sources thereof; dividing the supply of hydrocarbon gas into two portions; thoroughly mixing one portion of the hydrocarbon gas with air; burning ythe said mixture in the presence of an oxidation catalyst to produce a nitrogen-containing gas free from more than traces of carbon monoxide, oxygen, and hydrocarbons; intermittently thermally decomposing the other hydrocarbon portion in a self-sustaining cyclicalkv process whereby to produce hydrogen free from more than traces of oxygen and hydrocarbons; temporarily accumulatingthe hydrogen so produced to provide a source from which hydrogen can be Withdrawn continuously; passing a stream of said hydrogen in heat exchange relationship to, but not in direct contact with, a stream of said nitrogen-containing gas, whereby the two streams are brought to substantially the same temperature; thoroughly mixing in predetermined proportions the said hydrogen and nitrogen-containing gases to form a mixture in which the hydrogen is not more than about 15% of the mixture; and purifying the last-mentioned mixture to remove substantially all carbon dioxide AUGUSTUS B. KINZEL.`

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